Fluoroelastomers such as a copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP), and a terpolymer of tetrafluoroethylene (TFE), vinylidene fluoride (VDF), and hexafluoropropylene (HFP) have been used making seals, but their low temperature flexibility is not adequate for some seal applications.
There have been different approaches to improving the low temperature properties for fluoroelastomers.
U.S. Pat. No. 5,214,106 (Carlson et al.) describes substituting perfluoro alkyl vinyl ethers such as perfluoro methyl vinyl ether (CF2═CFOCF3) for the HFP in VDF/HFP/TFE (vinylidene fluoride/hexafluoropropylene/tetrafluoroethylene) copolymers to improve low temperature flexibility. However, these perfluorinated ethers can be expensive. U.S. Pat. No. 5,268,405 (Ojakaar et al.) discloses blending perfluoroelastomers with a perfluoropolyether in order to improve the low temperature properties of the composition. However, when the perfluoropolyether is mixed with a VDF/HFP/TFE copolymer, which has a glass transition temperature of −22° C., there is no improvement of glass transition temperature.
Further, although some literature references disclose improved low temperature properties of fluoroelastomeric compositions, the gum (i.e., the uncured fluropolymer) may not maintain the same low temperature properties upon curing. For example, U.S. Pat. No. 4,123,603 (Stewart) discloses a fluoroelastomer with improved low temperature properties by increasing VDF content in the polymer. Although the glass transition temperature of the polymer gum (VDF/HFP/TFE=60/28/12 wt %) in Example 1 of U.S. Pat. No. 4,123,603 was −27° C., the vulcanized compounded polymer with a bisphenol cure did not exhibit as low of a glass transition temperature as did the polymer gum according to a replicated example as shown in Example 3 of U.S. Pat. No. 5,175,223 (Brinati et al.).
In another application, a silicone-based pressure-sensitive adhesive is widely used as a pressure-sensitive adhesive having heat resistance. However, in the application to an electronic circuit or the like, particularly to a precision instrument and production process, such as hard disc drive (HDD), semiconductor devices (e.g. chemical vapor deposition(CVD) device) and electrodes (e.g. battery and fuel cell), when a silicone-based pressure-sensitive adhesive is used, a low molecular weight siloxane contained in the pressure-sensitive adhesive is released as an outgas into the atmosphere, and silicon dioxide produced resulting from oxidation of the siloxane gas sometimes causes a contact failure.
In order to avoid the above-described problem, development in an attempt to thermostabilize an acrylic pressure-sensitive adhesive that generates no siloxane gas is proceeding, but in view of the structure of a polymer component constituting the pressure-sensitive adhesive, heat resistance of an acrylic pressure-sensitive adhesive is generally far inferior to that of a silicon-based pressure-sensitive adhesive.
A fluorine-based material, such as fluororubber, is being used, for example, in an O-ring, a seal, a hose or a skid material and is excellent in mechanical property, heat resistance, weather resistance, chemical resistance and the like, but because of low adhesion, a pressure-sensitive adhesive composition having heat resistance and utilizing the characteristics of a fluororubber has been not obtained. To solve this problem, Japanese Unexamined Patent Publication No. 8-134422 has proposed a fluororubber-based pressure-sensitive adhesive composition with heat resistance, comprising 1) 100 parts by weight of a fluororubber polymer capable of peroxide crosslinking, 2) a catalytic amount of a peroxide, and 3) from 30 to 200 parts by weight of a fluororubber polymer incapable of peroxide crosslinking.
On the other hand, in a field completely different from a pressure-sensitive adhesive, development of an ionic liquid is proceeding. The ionic liquid that is also known as an ambient temperature molten salt, is liquid at normal temperature and due to its nonvolatility or high ion conductivity, is mainly used as an electrolytic solution in various electrochemical devices, such as a lithium secondary battery. In recent years, development of a gelled electrolyte using an ionic liquid is also studied for the purpose of preventing liquid leakage from a device. Furthermore, Japanese Patent No. 4597899 describes a gelled composition for heat dissipation, obtained by adding a thermally conductive inorganic filler and a gelling agent to an ionic liquid.